* Add mscs/hooks package, begin work for msc2836
* Flesh out hooks and add SQL schema
* Begin implementing core msc2836 logic
* Add test harness
* Linting
* Implement visibility checks; stub out APIs for tests
* Flesh out testing
* Flesh out walkThread a bit
* Persist the origin_server_ts as well
* Edges table instead of relationships
* Add nodes table for event metadata
* LEFT JOIN to extract origin_server_ts for children
* Add graph walking structs
* Implement walking algorithm
* Add more graph walking tests
* Add auto_join for local rooms
* Fix create table syntax on postgres
* Add relationship_room_id|servers to the unsigned section of events
* Persist the parent room_id/servers in edge metadata
Other events cannot assert the true room_id/servers for the
parent event, only make claims to them, hence why this is
edge metadata.
* guts to pass through room_id/servers
* Refactor msc2836 to allow handling from federation
* Add JoinedVia to PerformJoin responses
* Fix tests; review comments
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